This invention relates to parallel connected electrical load circuits and particularly automobile head light circuits. It provides a needed means for preventing failure of one light by the substitution of another energized lamp filament. Also included is an indication to the operator that the substitution has taken place and the original lamp is out.
The automobile operating at night with only one lighted head light is a common problem and safety hazard on the highway. In many instances the operator is unaware when one of the headlights on the vehicle goes out because of a filament failure. As the vehicle approaches an oncoming vehicle or pedestrian, the occupants of the other vehicle or the pedestrian, find it difficult to identify the shape or size of the oncoming vehicle, and are sometimes led to an incorrect decision in avoiding the oncoming vehicle with the headlight out. The danger in this situation is well recognized by the fact that in many jurisdictions it is a violation of the law to operate a vehicle with only one headlight operating.
Most over-the-road vehicles, such as automobiles are provided with more than one headlight. Usually each headlight is provided with two lamps, or two separately energized filaments. Usually one filament is constructed to burn relatively brightly and the other relatively dimly, with respect to each other.
Switches are provided to energize either the bright filament or the dim filament separately. In some instances a switch is provided to energize both simultaneously, although this is uncommon.
Usually the operator switches on the dim filament when operating the vehicle in the city environment and as the standard operating position for night time driving. On those occasions of country and freeway night driving, when other oncoming vehicles are not expected to be encountered and when driving at higher speeds, the operator switches over from the normal dim filament to the bright filament. Some vehicles provide a foot switch and some provide a manual switch to make the change. In the event of an oncoming car or other circumstances where the bright beam headlight may blind or glare in the face of others affecting their driving and activities, the legally required practice is to switch the bright beam off and return to the dim filament energized position.
In the past, various approaches have been disclosed to automatically energize a second or emergency lamp when the first or primary lamp fails. This problem has been addressed both from the circumstance of the vehicle with one headlight out, and from the general emergency situation where a primary electric load or light source fails and the emergency light source needs to be activated. Typical patents addressing the problem include U.S. Pat. Nos. 3,535,585--E. A. Barnum, 3,148,016--Fisher, U.S. Pat. No. 3,573,541--Dunn, et al., U.S. Pat. No. 3,659,179--Barker, et al., and U.S. Pat. No. 3,883,777--Morita.